It has already been proposed to substitute for conventional mechanical door locks, systems of various sorts in which a "key " is recognized by an electronic circuit which enables the locking bolt to be withdrawn. Since electronic circuits require power previously proposed electronic locks have required a battery to be incorporated in the lock housing, the provision of mains wiring to a lock being undesirable. If, however, a householder fails to change his lock battery it will be impossible to open the door from the outside and the householder may have to resort to breaking in to his own property.
The object of the present invention is to provide an electronic lock in which no battery or mains supply is required.